[ Apparently this thread wasn't on the lists, and I didn't even
notice. So re-sending the patches ]
On Sat, Jul 13, 2019 at 9:16 PM Eric W. Biederman <ebied...@xmission.com> wrote:
> Given that this fixes a regression and a bug.
>
> Acked-by: "Eric W. Biederman" <ebied...@xmission.com>
I'd much rather start from scratch. Like the attached.
Alexey Izbyshev has a third patch that then limits the setproctitle()
case to only allow looking into the env[] area, which looks
reasonable.
Linus
From 5563a2fb39fe0ad42f239d2f583128d50155002b Mon Sep 17 00:00:00 2001
From: Linus Torvalds <torva...@linux-foundation.org>
Date: Sat, 13 Jul 2019 13:40:13 -0700
Subject: [PATCH 1/2] /proc/<pid>/cmdline: remove all the special cases
Start off with a clean slate that only reads exactly from arg_start to
arg_end, without any oddities.
We'll add back the setproctitle() special case very differently in the
next commit.
Signed-off-by: Linus Torvalds <torva...@linux-foundation.org>
---
fs/proc/base.c | 71 ++++++--------------------------------------------
1 file changed, 8 insertions(+), 63 deletions(-)
diff --git a/fs/proc/base.c b/fs/proc/base.c
index 255f6754c70d..8040f9d1cf07 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -212,7 +212,7 @@ static int proc_root_link(struct dentry *dentry, struct path *path)
static ssize_t get_mm_cmdline(struct mm_struct *mm, char __user *buf,
size_t count, loff_t *ppos)
{
- unsigned long arg_start, arg_end, env_start, env_end;
+ unsigned long arg_start, arg_end;
unsigned long pos, len;
char *page;
@@ -223,36 +223,18 @@ static ssize_t get_mm_cmdline(struct mm_struct *mm, char __user *buf,
spin_lock(&mm->arg_lock);
arg_start = mm->arg_start;
arg_end = mm->arg_end;
- env_start = mm->env_start;
- env_end = mm->env_end;
spin_unlock(&mm->arg_lock);
if (arg_start >= arg_end)
return 0;
- /*
- * We have traditionally allowed the user to re-write
- * the argument strings and overflow the end result
- * into the environment section. But only do that if
- * the environment area is contiguous to the arguments.
- */
- if (env_start != arg_end || env_start >= env_end)
- env_start = env_end = arg_end;
-
- /* .. and limit it to a maximum of one page of slop */
- if (env_end >= arg_end + PAGE_SIZE)
- env_end = arg_end + PAGE_SIZE - 1;
-
/* We're not going to care if "*ppos" has high bits set */
- pos = arg_start + *ppos;
-
/* .. but we do check the result is in the proper range */
- if (pos < arg_start || pos >= env_end)
+ pos = arg_start + *ppos;
+ if (pos < arg_start || pos >= arg_end)
return 0;
-
- /* .. and we never go past env_end */
- if (env_end - pos < count)
- count = env_end - pos;
+ if (count > arg_end - pos)
+ count = arg_end - pos;
page = (char *)__get_free_page(GFP_KERNEL);
if (!page)
@@ -262,48 +244,11 @@ static ssize_t get_mm_cmdline(struct mm_struct *mm, char __user *buf,
while (count) {
int got;
size_t size = min_t(size_t, PAGE_SIZE, count);
- long offset;
- /*
- * Are we already starting past the official end?
- * We always include the last byte that is *supposed*
- * to be NUL
- */
- offset = (pos >= arg_end) ? pos - arg_end + 1 : 0;
-
- got = access_remote_vm(mm, pos - offset, page, size + offset, FOLL_ANON);
- if (got <= offset)
+ got = access_remote_vm(mm, pos, page, size, FOLL_ANON);
+ if (got <= 0)
break;
- got -= offset;
-
- /* Don't walk past a NUL character once you hit arg_end */
- if (pos + got >= arg_end) {
- int n = 0;
-
- /*
- * If we started before 'arg_end' but ended up
- * at or after it, we start the NUL character
- * check at arg_end-1 (where we expect the normal
- * EOF to be).
- *
- * NOTE! This is smaller than 'got', because
- * pos + got >= arg_end
- */
- if (pos < arg_end)
- n = arg_end - pos - 1;
-
- /* Cut off at first NUL after 'n' */
- got = n + strnlen(page+n, offset+got-n);
- if (got < offset)
- break;
- got -= offset;
-
- /* Include the NUL if it existed */
- if (got < size)
- got++;
- }
-
- got -= copy_to_user(buf, page+offset, got);
+ got -= copy_to_user(buf, page, got);
if (unlikely(!got)) {
if (!len)
len = -EFAULT;
--
2.22.0.193.g083935f9a2
From 63dd14999c6b210fbe33f780fec53faefa867d95 Mon Sep 17 00:00:00 2001
From: Linus Torvalds <torva...@linux-foundation.org>
Date: Sat, 13 Jul 2019 14:27:14 -0700
Subject: [PATCH 2/2] /proc/<pid>/cmdline: add back the setproctitle() special
case
This makes the setproctitle() special case very explicit indeed, and
handles it with a separate helper function entirely.
This makes the logic about when we use the string lengths etc much more
obvious, and makes it easy to see what we do.
[ Fixed for missing 'count' check noted by Alexey Izbyshev ]
Signed-off-by: Linus Torvalds <torva...@linux-foundation.org>
---
fs/proc/base.c | 54 +++++++++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 53 insertions(+), 1 deletion(-)
diff --git a/fs/proc/base.c b/fs/proc/base.c
index 8040f9d1cf07..3ad3ff4cc12c 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -209,12 +209,54 @@ static int proc_root_link(struct dentry *dentry, struct path *path)
return result;
}
+/*
+ * If the user used setproctitle(), we just get the string from
+ * user space at arg_start, and limit it to a maximum of one page.
+ */
+static ssize_t get_mm_proctitle(struct mm_struct *mm, char __user *buf,
+ size_t count, loff_t *ppos,
+ unsigned long arg_start)
+{
+ unsigned long pos = *ppos;
+ char *page;
+ int ret, got;
+
+ if (pos >= PAGE_SIZE)
+ return 0;
+
+ page = (char *)__get_free_page(GFP_KERNEL);
+ if (!page)
+ return -ENOMEM;
+
+ ret = 0;
+ got = access_remote_vm(mm, arg_start, page, PAGE_SIZE, FOLL_ANON);
+ if (got > 0) {
+ int len = strnlen(page, got);
+
+ /* Include the NUL character if it was found */
+ if (len < got)
+ len++;
+
+ if (len > pos) {
+ len -= pos;
+ if (len > count)
+ len = count;
+ len -= copy_to_user(buf, page+pos, len);
+ if (!len)
+ len = -EFAULT;
+ ret = len;
+ }
+ }
+ free_page((unsigned long)page);
+ return ret;
+}
+
static ssize_t get_mm_cmdline(struct mm_struct *mm, char __user *buf,
size_t count, loff_t *ppos)
{
unsigned long arg_start, arg_end;
unsigned long pos, len;
- char *page;
+ char *page, c;
/* Check if process spawned far enough to have cmdline. */
if (!mm->env_end)
@@ -228,6 +270,16 @@ static ssize_t get_mm_cmdline(struct mm_struct *mm, char __user *buf,
if (arg_start >= arg_end)
return 0;
+ /*
+ * Magical special case: if the argv[] end byte is not
+ * zero, the user has overwritten it with setproctitle(3).
+ *
+ * Possible future enhancement: do this only once when
+ * pos is 0, and set a flag in the 'struct file'.
+ */
+ if (access_remote_vm(mm, arg_end-1, &c, 1, FOLL_ANON) == 1 && c)
+ return get_mm_proctitle(mm, buf, count, ppos, arg_start);
+
/* We're not going to care if "*ppos" has high bits set */
/* .. but we do check the result is in the proper range */
pos = arg_start + *ppos;
--
2.22.0.193.g083935f9a2
